Several diseases appear to only strike the neural retina. Thus, there may be important proteins or other substances that are specific to the retina and which are abnormal either in function or concentration in these retinal diseases. Such a protein may be IRBP, the interphotoreceptor retinoid-binding protein. We have found a greatly decreased concentration of this protein in an early stage of hereditary retinal degeneration in the Abyssinian cat. Other proteins may not be retina-specific but possible defects in their synthesis and/or function may particularly affect retinal metabolism. Such a protein, the cAMP-dependent protein kinase, is found in many cell types but appears to have a defect in synthesis in retinoblastoma tumor cells grown in tissue culture. Such a defect could cause or contribute to the uncontrolled growth of retinoblastoma cells in vitro and perhaps in vivo as well.